Broadcast engineering

roadcast engineering is the field of electrical engineering, and now to some extent computer engineering and information technology, which deals with radio and television broadcasting. Audio engineering and RF engineering are also essential parts of broadcast engineering, being their own subsets of electrical engineering.

Broadcast engineering involves both the studio end and the transmitter end (the entire airchain), as well as remote broadcasts. Every station has a broadcast engineer, though one may now serve an entire station group in a city, or be a contract engineer who essentially freelances his services to several stations (often in small media markets) as needed.

The conversion to digital broadcasting means broadcast engineers must now be well-versed in digital television and digital radio, in addition to analogue principles. New equipment from the transmitter to the radio antenna to the receiver may be encountered by engineers new to the field. Furthermore, modern techniques place a greater demand on an engineer's expertise, such as sharing broadcast towers or radio antennas among different stations (diplexing).

Digital audio and digital video have revolutionized broadcast engineering in many respects.^[4] Broadcast studios and control rooms are now already digital in large part, using non-linear editing and digital signal processing for what used to take a great deal of time or money, if it was even possible at all. Mixing consoles for both audio and video are continuing to become more digital in the 2000s, as is the computer storage used to keep digital media libraries. Effects processing and TV graphics can now be done much more easily and professionally as well.

Other devices used in broadcast engineering are telephone hybrids, broadcast delays, and dead air alarms. See the glossary of broadcast engineering terms for further explanations

Audio engineering

Audio engineering is a part of audio science dealing with the recording and reproduction of sound through mechanical and electronic means. The field draws on many disciplines, including electrical engineering, acoustics, psychoacoustics, and music. Unlike acoustical engineering, audio engineering generally does not deal with noise control or acoustical design. However, an audio engineer is often closer to the creative and technical aspects of audio rather than formal engineering. An audio engineer must be proficient with different types of recording media, such as analog tape, digital multitrack recorders and workstations, and computer knowledge. With the advent of the digital age, it is becoming more and more important for the audio engineer to be versed in the understanding of software and hardware integration from synchronization to analog to digital transfers.

Educational technology

Educational technology is most simply and comfortably defined as an array of tools that might prove helpful in advancing student learning. Educational Technology relies on a broad definition of the word "technology". Technology can refer to material objects of use to humanity, such as machines or hardware, but it can also encompass broader themes, including systems, methods of organization, and techniques. Some modern tools include but are not limited to overhead projectors, laptop computers, and calculators. Newer tools such as "smartphones" and games (both online and offline) are beginning to draw serious attention for their learning potential.

Those who employ educational technologies to explore ideas and communicate meaning are learners or teachers.

Consider the Handbook of Human Performance Technology.^[2] The word technology for the sister fields of Educational and Human Performance Technology means "applied science." In other words, any valid and reliable process or procedure that is derived from basic research using the "scientific method" is considered a "technology." Educational or Human Performance Technology may be based purely on algorithmic or heuristic processes, but neither necessarily implies physical technology. The word technology, comes from the Greek "Techne" which means craft or art. Another word "technique", with the same origin, also may be used when considering the field Educational technology. So Educational technology may be extended to include the techniques of the educator

Information technology

Information technology (IT), as defined by the Information Technology Association of America (ITAA), is "the study, design, development, implementation, support or management of computer-based information systems, particularly software applications and computer hardware."^[1] IT deals with the use of electronic computers and computer software to convert, store, protect, process, transmit, and securely retrieve information.

Today, the term information technology has ballooned to encompass many aspects of computing and technology, and the term has become very recognizable. The information technology umbrella can be quite large, covering many fields. IT professionals perform a variety of duties that range from installing applications to designing complex computer networks and information databases. A few of the duties that IT professionals perform may include data management, networking, engineering computer hardware, database and software design, as well as the management and administration of entire systems.

When computer and communications technologies are combined, the result is information technology, or "infotech". Information Technology (IT) is a general term that describes any technology that helps to produce, manipulate, store, communicate, and/or disseminate information. Presumably, when speaking of Information Technology (IT) as a whole, it is noted that the use of computers and information are associated.

The term Information Technology (IT) is sometimes said to have been coined by Jim Domsic of Michigan in November 1981.^{[citation needed]} Domsic, who worked as a computer manager for an automotive related industry, is supposed to have created the term to modernize the outdated phrase "data processing". The Oxford English Dictionary, however, in defining information technology as "the branch of technology concerned with the dissemination, processing, and storage of information, esp. by means of computers" provides an illustrative quote from the year 1958 (Leavitt & Whisler in Harvard Business Rev. XXXVI. 41/1 "The new technology does not yet have a single established name. We shall call it information technology.") that predates the so-far unsubstantiated Domsic coinage.

In recent years ABET and the ACM have collaborated to form accreditation and curriculum standards for degrees in Information Technology as a distinct field of study separate from both Computer Science and Information Systems. SIGITE is the ACM working group for defining these standards.

Information and communication technologies

ICT capabilities vary widely from the sophistication of major western economies to lesser provision in the developing world. But the latter are catching up fast, often leapfrogging older generations of technology and developing new solutions that match their specific needs.

The expression "information and communication technologies" cannot refer only to contemporary automated technological artefacts. Paper-based writing, being itself a technology (Ong, 1988: Chapter 4), can also be included in such ontological category, as can pre-digital means of generating, transmitting and archiving sonic utterances. The common usage of the term, as stated without further investigation, does not warrant its encyclopaedic mention.

The ICT may not survive in its present form for long. Sooner than later developing countries would get over the PC mania prevalent now in the developed world, unless there is a remarkable change in the economy of owning a PC. Any technology that requires the masses to own a PC, in its present form, to access information is unlikely to be successful in the foreseeable future. Possibilities appear to exist, however, in the mobile phone technology, which is fast becoming very affordable by the masses, is voice based and can be integrated with the Information Technology at the server end of a computer network. For example, in the field of education ^[1] people can ask question through a mobile phone, a database of answers to such questions can be generated using the technologies used currently in Wikipedia and call centers and the text in these databases could be converted into voice, by developing text to voice technologies in the various languages. The person seeking information can be informed when the answer is available and better answers sought based on his/her feedback. The emerging 3G and 4G mobile phone technologies can indeed facilitate such developments. An alternative technology could be to integrate the mobile phone with the television screen, so that visual information can be viewed easily. Similarly, there is a possibility for developing interactive radio, on the lines of interactive TV.

Environmental Engineering Science

Students in Environmental Engineering Science typically combine scientific studies of the biosphere with mathematical, analytical and design tools found in the engineering fields

Environmental Engineering Science (EES) is a multidisciplinary field of engineering that combines the biological, chemical and physical sciences with the field of engineering. This major traditionally requires the student to take many basic engineering classes in fields such as thermodynamics, advanced math, computer modeling and simulation as well as technical classes in subjects such as statics, mechanics, hydrology, and fluid dynamics. As the student progresses, the upper division elective classes define a specific field of study for the student with a choice in a wide range of science, technology and engineering related classes^[1]:

Engineering physics

Engineering physics (EP) is an academic degree, available mainly at the levels of B.Sc., M.Sc. and Ph.D. Unlike other engineering degrees (such as aerospace engineering or electrical engineering), EP does not necessarily include a particular branch of science or physics. Instead, EP is meant to provide a more thorough grounding in applied physics of any area chosen by the student (such as optics, nanotechnology, mechanical engineering, electrical engineering, control theory, aerodynamics, or solid-state physics). This is why in some countries only the B.Sc. part of the degree is called a degree in Engineering Physics.

Engineering physics degrees are respected degrees taught in many countries. It is notable that in many languages the term for Engineering Physics would be directly translated into English as "technical physics". In some countries, both what would be translated as "Engineering physics" and what would be translated as "Technical physics" are disciplines leading to academic degrees, with the former specializes in nuclear power research,^[1] and the latter closer to engineering physics.^[2]

More recently, as an apparent attempt to stress the interdisciplinary nature of such degrees, some institutions now use the term Engineering science.

Energy storage

Energy storage mediums are matter that store some form of energy that can be drawn upon at a later time to perform some useful operation. A device that stores energy is sometimes called an accumulator. All forms of energy are either potential energy (eg. chemical, gravitational or electrical energy) or kinetic energy (eg. thermal energy). A wind up clock stores potential energy (in this case mechanical, in the spring tension), a battery stores readily convertible chemical energy to keep a clock chip in a computer running (electrically) even when the computer is turned off, and a hydroelectric dam stores power in a reservoir as gravitational potential energy. Ice storage tanks store ice (thermal energy)at night to meet peak demand for cooling . Even food is a form of energy storage, chemical in this case.

Energy

In physics, energy (from the Greek ἐνέργεια - energeia, "activity, operation", from ἐνεργός - energos, "active, working"^[1]) is a scalar physical quantity that describes the amount of work that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law. Several different forms of energy exist to explain all known natural phenomena. These forms include (but are not limited to) kinetic, potential, thermal, gravitational, sound, light, elastic, and electromagnetic energy. The forms of energy are often named after a related force.

Any form of energy can be transformed into another form, but the total energy always remains the same. This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time.^[2]

Although the total energy of a system does not change with time, its value may depend on the frame of reference. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the Earth

A wave of diverse acts

Electronica was made possible by advancements in music technology, especially electronic musical instruments, synthesizers, music sequencers, drum machines, digital audio workstations^{[citation needed]}. Early forms of electronic music required large amounts of complex equipment and multiple operators for live performances, and multiple engineers to record the music at high quality.^{[citation needed]} As the technology developed, it became possible for individuals or smaller groups to produce electronic songs and recordings in smaller studios, even in project studios. At the same time, computers facilitated the use of music "samples" and "loops" as construction kits for sonic compositions. ^[7] This led to a period of creative experimentation and the development of new forms, some of which became known as electronica. ^[5][8]

In the mid-1990s, electronica began to be used by MTV and major record labels to describe mainstream electronic dance music made by such artists as Orbital (who had previously been described as ambient) and The Prodigy.^{[citation needed]} It is currently used to describe a wide variety of musical acts and styles, linked by a penchant for overtly electronic production; ^[9] a range which includes more popular acts such as Björk, Goldfrapp and Braindance artists such as Autechre, Aphex Twin, and Boards of Canada^[3] to dub-oriented downtempo, downbeat, and trip-hop. Madonna and Björk are said to be responsible for electronica's thrust into mainstream culture, with their albums Ray of Light (Madonna),^[6] Post and Homogenic (Björk). Electronica artists that would later become commercially successful began to record in this early 1990s period, before the term had come into common usage, including for example Fatboy Slim, Fœtus, Daft Punk, The Chemical Brothers, The Crystal Method, Moby, and Underworld. ^[10] A focus on "songs", a fusion of styles and a combination of traditional and electronic instruments often sets apart musicians working in electronic-styles over more straight-ahead styles of house, techno and trance.^{[citation needed]} Electronica composers often create alternate versions of their compositions, known as "remixes"; this practice also occurs in related musical forms such as ambient, jungle, and electronic dance music. ^[11] Wide ranges of influences, both sonic and compositional, are combined in electronica recordings.

ATSC standalone DVD recorders

As a result of the North American digital switchover, tuner-equipped devices manufactured or imported into the United States are now required by the US Federal Communications Commission to include digital tuners.

This has caused most new VHS recorders to be implemented as DVD/VCR combo units, or to be manufactured without tuners. The US requirement of ATSC compatibility forces inclusion of MPEG-2 decoding hardware, which is already part of all DVD players but which otherwise would not have been needed in an analog-only VCR.

An ATSC-capable DVD unit can also serve as a more-powerful alternative to digital television adapters, which allow DTV reception with older NTSC analog televisions. The DVD recorders offer additional capabilities, such as automated VCR-style timeshifting of programming and a variety of output formats, that are deliberately not included in the most common mass-market US ATSC converters.

Unlike the more common digital television adapter boxes, DVD recorder units are able to tune both analog and digital signals - an advantage when receiving low-power television and foreign signals. Some, however, do suffer from many of the same design limitations as the less costly converter boxes, including poorly-designed signal strength meters, incomplete display of broadcast program information, incompatibility with antenna rotators or CEA-909 smart antennas and inability to add digital channels without wiping out all existing channels and rescanning the entire band. A DVD recording of an over-the-air HDTV broadcast is at DVD resolution, which is inferior to the original broadcast with 720p or 1080i resolution. Some units also provide limited USB or flash memory interface capability, often only supporting viewing of digital camera still photos or playback of MP3's with no ability to write video to these media.

Standalone DVD recorders

When the standalone DVD recorder first appeared on the Japanese consumer market in 1999, these early units were very expensive, costing between $2500 and $4000 USD. However, as of early 2007, DVD recorders from notable brands are selling for US$200 or €150 and less, with even lower "street prices". Early units supported only DVD-RAM and DVD-R discs, but the more recent units can record to all major formats DVD-R, DVD-RW, DVD+R, DVD+RW, and DVD+R DL. Some models now include hard disk-based digital video recorders (DVRs) to improve ease of use. Standalone DVD recorders generally have basic DVD authoring software built in; however, the appearance of the finished DVD is very basic and usually completely under the control of the unit.

Some believed that DVD recorders would supersede the VCR as the standard television-recording device; however, with the rise of DVR's and competing media formats like Blu-ray, the DVD recorder's future seems limited

Computer-based DVD drives

DVD recorder drives have become standard equipment in many, though not all, computer systems currently on the market, after being initially popularized by the Pioneer/Apple SuperDrive; aftermarket drives as of early 2007 can cost as little as $23 [2]. DVD recorder drives can be used in conjunction with DVD authoring software to create DVDs near or equal to commercial quality, and are also widely used for data backup and exchange. As a general rule, computer-based DVD recorders can also handle CD-R and CD-RW media; in fact, a number of standalone DVD recorders actually use drives designed for computers.

Most internal drives are designed with parallel ATA interfaces, with serial ATA becoming more readily available. External drives almost always use USB 2.0 or IEEE 1394, with eSATA becoming an option as well.

DVD recorder drives are required^{[by whom?]}to respect DVD region codes when reading a disc, but do not impose a region code on written discs unless the code has specifically been written into the disc's content.

DVD duplication systems are generally built out of stacks of these drives, connected through a computer-based backplane

Technical information

Originally, DVD recorders supported one of three standards: DVD-RAM, DVD-RW (using DVD-VR), and DVD+RW (using DVD+VR), none of which are directly compatible. As a general rule, however, most current drives support both the + and - standards, while few support the DVD-RAM standard, which is not directly compatible with standard DVD readers.

Recording speed is generally denoted in values of X (similar to CD-ROM usage), where 1X in DVD usage is equal to 1.321 MB/s, roughly equivalent to a 9X CD-ROM. In practice, this is largely confined to computer-based DVD recorders, since standalone units generally record in real time, that is, 1X speed.

DVD recorders use a laser (usually 650 nm red) to read and write DVDs. The reading laser is usually not stronger than 5 mW, while the writing laser is considerably more powerful. The faster the writing speed is rated, the stronger the laser is. DVD burner lasers often peak at about 100-400 mW in continuous wave (some are pulsed). Some laser hobbyists have discovered ways to extract the laser diode from DVD burners

DVD recorder

A DVD recorder (also known as a DVDR, mainly outside of the UK and Ireland), is an optical disc recorder that records video onto blank writeable DVD media. Such devices are available as either installable drives for computers or as standalone components for use in studios or home theatre systems.

As of March 1, 2007 all new tuner-equipped television devices manufactured or imported in the United States must include digital tuners. The US Federal Communications Commission has interpreted this rule broadly so as to include apparatus such as computer video capture cards, videotape recorders and standalone DVD recorders. NTSC DVD recorders are therefore undergoing a transformation, either adding a digital ATSC tuner or removing over-the-air television tuner capability entirely.

Environment

Many consumer electronics have planned obsolescence, resulting in E-waste. It is estimated that during 2003 the US alone generated over 2.8 million tons of electronic waste. Less than 10% of that amount was recovered (reused or recycled).

Standby power used by consumer electronics and appliance while they are turned off accounts for 5 to 10% of household energy consumption, adding an estimated $3 billion to annual energy costs in the USA. "In the average home, 75% of the electricity used to power home electronics is consumed while the products are turned off.

Connectivity

A recent trend in many types of consumer electronics is connectivity. It's usual for many products to include Internet connectivity using technologies such as Wi-Fi, Bluetooth or Ethernet. Many products not traditionally associated with computer use (such as TVs or Hi-Fi equipment) now provide options to connect to the Internet or to a computer using a home network to provide access to digital content.

The desire to connect CE products capable of displaying High definition (HD) content has lead the industry to develop a number of technologies, such as WirelessHD or ITU-T G.hn, which are optimized for distribution of HD content between CE devices in a home

Product convergence

While consumer electronics continues in its trend of convergence, combining elements of many consumer electronic items, the consumer faces different decisions when purchasing their items. There is an ever increasing need to keep the product information updated and most comparable, for the consumer to be able to make an informed buying decision. The variables are becoming more about 'style and price' rather than 'specification and performance'. This convergence of technologies promises a shrinking of choice of retailer to the consumer and the rise of manufacturer status within the home. There is a gradual shift towards e-commerce web-storefronts.

Ever-falling prices

One overriding characteristic of all consumer electronic products is the trend of ever-falling prices. This is driven by gains in manufacturing efficiency and automation, lower labor costs as manufacturing has moved to lower-wage countries, and improvements in semiconductor design. Semiconductor components benefit from Moore's Law, an observed principle which states that, for a given price, semiconductor functionality doubles every 18 months.

Consumer electronics

Consumer electronics include electronic equipment intended for everyday use. Consumer electronics are most often used in entertainment, communications and office productivity. Some products classed as consumer electronics include personal computers, telephones, MP3 players, audio equipment, televisions, calculators, GPS automotive navigation systems and playback and recording of video media such as DVDs, VHSs or camcorders. The global consumer electronics industry is dominated by American, Japanese and South Korean companies.

The CEA (Consumer Electronics Association) estimates 2007 Consumer Electronics sales at 150 billion dollars.^[1]

Consumer electronics are manufactured throughout the world, although there is a particularly high concentration of manufacturing activity in Japan and South Korea. The latest consumer electronics are previewed yearly at the Consumer Electronics Show in Las Vegas, Nevada, at which many industry pioneers speak.

Miscellaneous

Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors which can contain more than a 100 million gates. In practice, the gates are made from field-effect transistors (FETs), particularly MOSFETs.

Compound logic gates AND-OR-Invert (AOI) and OR-AND-Invert (OAI) are often employed in circuit design because their construction using MOSFET's is simpler and more efficient than the sum of the individual gates.^[2]

In reversible logic, Toffoli gates are used.

Three-state logic gates

Three-state, or 3-state, logic gates have three states of the output: high (H), low (L) and high-impedance (Z). The high-impedance state plays no role in the logic, which remains strictly binary. These devices are used on buses to allow multiple chips to send data. A group of three-states driving a line with a suitable control circuit is basically equivalent to a multiplexer, which may be physically distributed over separate devices or plug-in cards.

In electronics, a high output would mean the output is sourcing current from the positive power terminal (positive voltage). A low output would mean the output is sinking current to the negative power terminal (zero voltage). High impedance would mean that the output is effectively disconnected from the circuit.

'Tri-state', a widely-used synonym of 'three-state', is a trademark of the National Semiconductor Corporation

Storage of bits

Related to the concept of logic gates (and also built from them) is the idea of storing a bit of information. None of the gates discussed up to here can store a value by itself: when the inputs change, the outputs immediately react. It is possible to make a storage element either through a capacitor (which stores charge due to its physical properties) or by feedback. Connecting the output of a gate to the input causes it to be put through the logic again, and choosing the feedback correctly allows it to be preserved or modified through the use of other inputs. A set of gates arranged in this fashion is known as a "latch", and more complicated designs that utilize clock signals and change only on the rising edge are called edge-triggered "flip-flops". The combination of multiple flip-flops in parallel, to store a multiple-bit value, is known as a register. When using any of these gate setups the overall system has memory; it is then called a sequential logic system since its output can be influenced by its previous state(s).

These registers or capacitor-based circuits are known as computer memory. They vary in performance, based on factors of speed, complexity, and reliability of storage, and many different types of designs are used based on the application

De Morgan equivalent symbols

By use of De Morgan's theorem, an AND gate can be turned into an OR gate by inverting the sense of the logic at its inputs and outputs. This leads to a separate ends can be replaced by a simple bubble-less connection and a suitable change of gate. If the NAND is drawn as OR with input bubbles, and a NOR as AND with input bubbles, this gate substitution occurs automatically in the diagram (effectively, bubbles "cancel"). This is commonly seen in real logic diagrams - thus the reader must not get into the habit of associating the shapes exclusively as OR or AND shapes, but also take into account the bubbles at both inputs and outputs in order to determine the "true" logic function indicated.

All logic relations can be realized by using NAND gates. (This can also be done using NOR gates). De Morgan's theorem is most commonly used to transform all logic gates to NAND gates or NOR gates. This is done mainly since it is easy to buy logic gates in bulk and because many electronics labs stock only NAND and NOR gates.

Symbols

There are two sets of symbols in common use, both now defined by ANSI/IEEE Std 91-1984 and its supplement ANSI/IEEE Std 91a-1991. The "distinctive shape" set, based on traditional schematics, is used for simple drawings and is quicker to draw by hand. It is sometimes unofficially described as "military", reflecting its origin if not its modern usage. The "rectangular shape" set, based on IEC 60617-12, has rectangular outlines for all types of gate, and allows representation of a much wider range of devices than is possible with the traditional symbols. The IEC's system has been adopted by other standards, such as EN 60617-12:1999 in Europe and BS EN 60617-12:1999 in the United Kingdom.

The goal of IEEE Std 91-1984 was to provide a uniform method of describing the complex logic functions of digital circuits with schematic symbols. These functions were more complex than simple AND and OR gates. They could be medium scale circuits such as a 4-bit counter to a large scale circuits such as a microprocessor. The 1984 version did not include the "distinctive shape" symbols.[1] These were added to the 1991 supplement with this note: "The distinctive-shape symbol is, according to IEC Publication 617, Part 12, not preferred, but is not considered to be in contradiction to that standard."

In the 1980s, schematics were the predominant method to design both circuit boards and custom ICs known as gate arrays. Today custom ICs and the field-programmable gate array are typically designed with Hardware Description Languages (HDL) such as Verilog or VHDL. The need for complex logic symbols has diminished and distinctive shape symbols are still the predominate style.^{[citation needed]}

Type	Distinctive shape	Rectangular shape	Boolean algebra between A & B	Truth table
AND				INPUT OUTPUT A B A AND B 0 0 0 0 1 0 1 0 0 1 1 1
OR			A + B	INPUT OUTPUT A B A OR B 0 0 0 0 1 1 1 0 1 1 1 1
NOT				INPUT OUTPUT A NOT A 0 1 1 0
In electronics a NOT gate is more commonly called an inverter. The circle on the symbol is called a bubble, and is generally used in circuit diagrams to indicate an inverted (active-low) input or output.[1]
NAND				INPUT OUTPUT A B A NAND B 0 0 1 0 1 1 1 0 1 1 1 0
NOR				INPUT OUTPUT A B A NOR B 0 0 1 0 1 0 1 0 0 1 1 0
XOR				INPUT OUTPUT A B A XOR B 0 0 0 0 1 1 1 0 1 1 1 0
XNOR				INPUT OUTPUT A B A XNOR B 0 0 1 0 1 0 1 0 0 1 1 1

In practice, the cheapest gate to manufacture is usually the NAND gate. Additionally, Charles Peirce showed that NAND gates alone (as well as NOR gates alone) can be used to reproduce the functions of all the other logic gates.

The 7400 chip, containing four NANDs. The two additional pins supply power (+5 V) and connect the ground.

Two more gates are the exclusive-OR or XOR function and its inverse, exclusive-NOR or XNOR. The two input Exclusive-OR is true only when the two input values are different, false if they are equal, regardless of the value. If there are more than two inputs, the gate generates a true at its output if the number of trues at its input is odd ([2]). In practice, these gates are built from combinations of simpler logic gates

Logic gates

NAND and NOR logic gates are the two pillars of logic, in that all other types of Boolean logic gates (i.e., AND, OR, NOT, XOR, XNOR) can be created from a suitable network of just NAND or just NOR gate(s). They can be built from relays or transistors, or any other technology that can create an inverter and a two-input AND or OR gate. Hence the NAND and NOR gates are called the universal gates.

For an input of 2 variables, there are 16 possible boolean algebraic functions. These 16 functions are enumerated below, together with their outputs for each combination of inputs variables.

INPUT	A	0	0	1	1		Meaning
	B	0	1	0	1
OUTPUT	FALSE	0	0	0	0		Whatever A and B, the output is false. Contradiction.
	A AND B	0	0	0	1		Output is true if and only if (iff) both A and B are true.
	A B	0	0	1	0		A doesn't imply B. True iff A but not B.
	A	0	0	1	1		True whenever A is true.
	A B	0	1	0	0		A is not implied by B. True iff not A but B.
	B	0	1	0	1		True whenever B is true.
	A XOR B	0	1	1	0		True iff A is not equal to B.
	A OR B	0	1	1	1		True iff A is true, or B is true, or both.
	A NOR B	1	0	0	0		True iff neither A nor B.
	A XNOR B	1	0	0	1		True iff A is equal to B.
	NOT B	1	0	1	0		True iff B is false.
	A B	1	0	1	1		A is implied by B. False if not A but B, otherwise true.
	NOT A	1	1	0	0		True iff A is false.
	A B	1	1	0	1		A implies B. False if A but not B, otherwise true.
	A NAND B	1	1	1	0		A and B are not both true.
	TRUE	1	1	1	1		Whatever A and B, the output is true. Tautology.

The four functions denoted by arrows are the logical implication functions. These functions are generally less common, and are usually not implemented directly as logic gates, but rather built out of gates like AND and OR

Background

Main article: Logic family

The simplest form of electronic logic is diode logic. This allows AND and OR gates to be built, but not inverters, and so is an incomplete form of logic. Further, without some kind of amplification it is not possible to have such basic logic operations cascaded as required for more complex logic functions. To build a functionally complete logic system, relays, valves (vacuum tubes), or transistors can be used. The simplest family of logic gates using bipolar transistors is called resistor-transistor logic, or RTL. Unlike diode logic gates, RTL gates can be cascaded indefinitely to produce more complex logic functions. These gates were used in early integrated circuits. For higher speed, the resistors used in RTL were replaced by diodes, leading to diode-transistor logic, or DTL. It was then discovered that one transistor could do the job of two diodes in the space of one diode even better, by more quickly switching off the following stage, so transistor-transistor logic, or TTL, was created. In virtually every type of contemporary chip implementation of digital systems, the bipolar transistors have been replaced by complementary field-effect transistors (MOSFETs) to reduce size and power consumption still further, thereby resulting in complementary metal–oxide–semiconductor (CMOS) logic.

For small-scale logic, designers now use prefabricated logic gates from families of devices such as the TTL 7400 series by Texas Instruments and the CMOS 4000 series by RCA, and their more recent descendants. Increasingly, these fixed-function logic gates are being replaced by programmable logic devices, which allow designers to pack a large number of mixed logic gates into a single integrated circuit. The field-programmable nature of programmable logic devices such as FPGAs has removed the 'hard' property of hardware; it is now possible to change the logic design of a hardware system by reprogramming some of its components, thus allowing the features or function of a hardware implementation of a logic system to be changed

Logic gate

A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits. Logic gates are primarily implemented electronically using diodes or transistors, but can also be constructed using electromagnetic relays, fluidics, optics, molecules, or even mechanical elements.

In electronic logic, a logic level is represented by a voltage or current, (which depends on the type of electronic logic in use). Each logic gate requires power so that it can source and sink currents to achieve the correct output voltage. In logic circuit diagrams the power is not shown, but in a full electronic schematic, power connections are required

Digital electronics

Digital electronics are electronics systems that use digital signals. Digital electronics are representations of Boolean algebra (also see truth tables) and are used in computers, mobile phones, and other consumer products. In a digital circuit, a signal is represented in one of two states or logic levels. The advantages of digital techniques stem from the fact it is easier to get an electronic device to switch into one of two states, than to accurately reproduce a continuous range of values.

Digital electronics or any digital circuit are usually made from large assemblies of logic gates, simple electronic representations of Boolean logic functions.

To most electronic engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits.

Circuit design

The process of circuit design can cover systems ranging from complex electronic systems all the way down to the individual transistors within an integrated circuit. For simple circuits the design process can often be done by one person without needing a planned or structured design process, but for more complex designs, teams of designers following a systematic approach with intelligently guided computer simulation are becoming increasingly common.

Formal circuit design usually involves the following stages:

• sometimes, writing the requirement specification after liaising with the customer
• writing a technical proposal to meet the requirements of the customer specification
• synthesising on paper a schematic circuit diagram, an abstract electrical or electronic circuit that will meet the specifications
• calculating the component values to meet the operating specifications under specified conditions
• performing simulations to verify the correctness of the design
• building a breadboard or other prototype version of the design and testing against specification
• making any alterations to the circuit to achieve compliance
• choosing a method of construction as well as all the parts and materials to be used
• presenting component and layout information to draughtspersons, and layout and mechanical engineers, for prototype production
• testing or type-testing a number of prototypes to ensure compliance with customer requirements
• signing and approving the final manufacturing drawings

Inherent noise

Analogue systems invariably include noise; that is, random disturbances or variations, some caused by the random thermal vibrations of atomic particles. Since all variations of an analogue signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise. As the signal is copied and re-copied, or transmitted over long distances, these random variations become more significant and lead to signal degradation. Other sources of noise may come from external electrical signals, or poorly designed components. These disturbances are reduced by shielding, and using low-noise amplifiers

Analogue electronics

An analogue signal uses some attribute of the medium to convey the signal's information. For example, an aneroid barometer uses angular position as the signal to convey pressure information. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form ( such as sound, light, temperature, pressure, position) to an electrical signal by a transducer.

The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. In such a system 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees.

Another method of conveying an analogue signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as changing the phase of the carrier signal are also used.

In an analogue sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape

Construction methods

Many different methods of connecting components have been used over the years. For instance, early electronics often used point to point wiring with components attached to wooden breadboards to construct circuits. Cordwood construction and wire wraps were other methods used. Most modern day electronics now use printed circuit boards (made of FR4), and highly integrated circuits. Health and environmental concerns associated with electronics assembly have gained increased attention in recent years, especially for products destined to the European Union, with its Restriction of Hazardous Substances Directive (RoHS) and Waste Electrical and Electronic Equipment Directive (WEEE), which went into force in July 2006.

Computer aided design (CAD)

Today's electronics engineers have the ability to design circuits using premanufactured building blocks such as power supplies, semiconductors (such as transistors), and integrated circuits. Electronic design automation software programs include schematic capture programs and printed circuit board design programs. Popular names in the EDA software world are NI Multisim, Cadence (ORCAD), Eagle PCB and Schematic, Mentor (PADS PCB and LOGIC Schematic), Altium (Protel), LabCentre Electronics (Proteus) and many others